emailrelay-check-ipaddress.pl

#!/usr/bin/env perl
#
# SPDX-FileCopyrightText: 2026 Graeme Walker <graeme_walker@users.sourceforge.net>
# SPDX-License-Identifier: FSFAP
#
# Copyright (c) 2026 Graeme Walker <graeme_walker@users.sourceforge.net>
#
# Copying and distribution of this file, with or without modification,
# are permitted in any medium without royalty provided the copyright
# notice and this notice are preserved.  This file is offered as-is,
# without any warranty.
# ===
#
# emailrelay-check-ipaddress.pl
#
# An example E-MailRelay filter script that verifies the
# submitting client's IP address. The IP address is read
# from the envelope file. Invalid IP addresses are rejected
# by deleting the two message files and exiting with the
# special exit code of 100. Note that this checks the IP
# address very late in the submission process; a firewall
# or DNSBL check might work better.
#

use strict ;
use warnings ;
use IO::File ;
$SIG{__DIE__} = sub { (my $e = join(" ",@_)) =~ s/\n/ /g ; print "<<error>>\n<<error: $e>>\n" ; exit 99 } ;

my %allow = (
    "127.0.0.1" => 1 ,
    "1.1.1.1" => 1 ,
    # etc
) ;

my $content = $ARGV[0] or die "usage error\n" ;
my $envelope = $ARGV[1] or die "usage error\n" ;
my $fh = new IO::File( $envelope ) or die "cannot open envelope file: $!\n" ;
my $txt ;
{
    local $/ = undef ;
    $txt = <$fh> ;
}
my ( $ip ) = ( $txt =~ m/X-MailRelay-Client: (\S*)/m ) ;
if( $allow{$ip} )
{
    exit( 0 ) ;
}
else
{
    print "<<not allowed>>\n<<not allowed: $ip>>\n" ;
    unlink( $content ) ;
    unlink( $envelope ) ;
    exit( 100 ) ;
}